1. Field of the Invention
The present invention relates to an optical scanning device and an image forming apparatus, and more particularly, to an optical scanning device that scans a scanning surface with a light beam and an image forming apparatus including the optical scanning device.
2. Description of the Related Art
For electrophotographic image recording, an image forming apparatus using a laser as a light source is widely used. Such an image forming apparatus includes an optical scanning device in which a light beam (a scanning light beam) emitted from the light source is deflected by a deflector to scan a surface of a photosensitive drum with the light beam by which a latent image is formed on the surface of the photosensitive drum.
Such an image forming apparatus has a problem that shading may appear on an output image because optical intensities of scanning light beams vary with a change in temperature or over time. To cope with this problem, an optical scanning device using a conventional edge emitting laser performs an automatic power control (APC) while monitoring optical intensity of a light beam emitted from the other facet of the laser. However, in an optical scanning device using a vertical cavity surface emitting laser (VCSEL), because the VCSEL only emits a light beam from the top surface, it is configured that a light receiving element such as a photodiode receives a portion of a light beam emitted from the VCSEL to monitor optical intensity of the light beam (hereinafter, “a monitoring light beam”), and the optical scanning device performs the APC based on the optical intensity of the monitoring light beam (for example, see Japanese Patent Application Laid-open No. 2002-40350, Japanese Patent Application Laid-open No. 2006-91157, Japanese Patent Application Laid-open No. 2005-156933, and Japanese Patent Application Laid-open No. 2006-259098).
Generally, air flows inside an optical scanning device or inside an image forming apparatus, and in which dust or dirt flies with the airflow. If dust or dirt is attached to a light receiving element or a laser chip, optical intensity of a light beam traveling toward a scanning surface may be affected.
For example, there has been developed an apparatus using a surface emitting laser as a light source. The apparatus is arranged on an optical path of a light beam emitted from the surface emitting laser, and splits the incident light beam so as to use a portion of the light beam as a monitoring light beam (for example, see Japanese Patent Application Laid-open No. H8-33061). In such an apparatus, a light receiving element that receives the monitoring light beam is exposed to the air in which dust or dirt constantly exists. Therefore, it is highly likely that the dust or dirt is attached to a light receiving surface of the light receiving element, resulting in degradation of the monitoring performance.